Recent studies with rodent Experimental Autoimmune Encephalitis (EAE) models of Multiple Sclerosis (MS) suggest phospholipase A2 (PLA2) enzymes are involved in the genesis of both the behavioral deficits and the inflammation that characterize this disease (Pinto, et al., 2003; Kalyvas and David, 2004). Systemic sPLA2 enzymes in particular were inhibited in one of these studies by infusion of large molecule sPLA2 substrate decoys. The result was significant behavioral improvement and reduced inflammation.
Multiple sclerosis (MS) is a debilitating, inflammatory, neurological illness characterized by demyelination of the central nervous system. The disease primarily affects young adults with a higher incidence in females. Symptoms of the disease include fatigue, numbness, tremor, tingling, dysesthesias, visual disturbances, dizziness, cognitive impairment, urological dysfunction, decreased mobility, and depression. Four types classify the clinical patterns of the disease: relapsing-remitting, secondary progressive, primary-progressive and progressive-relapsing (S. L. Hauser and D. E. Goodkin, Multiple Sclerosis and Other Demyelinating Diseases in Harrison's Principles of Internal Medicine 14.sup.th Edition, vol. 2, Mc Graw-Hill, 1998, pp. 2409-2419).
The exact etiology of MS is unknown; however, it is strongly suspected that the demyelination characteristic of the disease is the result of an autoimmune response, perhaps triggered by an environmental insult, e.g. a viral infection. Specifically, it is hypothesized that MS is caused by a T-cell-mediated, autoimmune inflammatory reaction. The autoimmune basis is strongly supported by the fact that antibodies specific to myelin basic protein (MBP) have been found in the serum and cerebrospinal fluid of MS patients, and these antibodies, along with T-cells that are reactive to MBP and other myelin proteolipids, increase with disease activity. Furthermore, at the cellular, level it is speculated that T-cell proliferation and other cellular events, such as activation of B cells and macrophages and secretion of cytokines accompanied by a breakdown of the blood-brain barrier, can cause destruction of myelin and oligodendrocytes. (R. A. Adams, M. V. Victor and A. H. Ropper eds, Principles of Neurology, Mc Graw-Hill, New York, 1997, pp. 903-921). Progressive MS (primary and secondary) may be based on a neurodegenerative process occurring with demyelination.
The pathophysiology of Multiple Sclerosis involves both antigen specific mechanisms and the innate immune system, including several elements of the inflammatory response. MS is not unusual in this regard since inflammation is now recognized as a contributing factor in all disorders in which there is destruction of nervous tissue. Increased hydrolysis of membrane phospholipids by phospholipase A2 is a well-known early response to tissue damage in all organ systems including the nervous system. The activity of these enzymes regulates levels of inflammatory mediators including prostaglandins, leukotrienes, fatty acids, and reactive oxygen species. All these mediators are produced in the early stages of neurodegeneration, regardless of its cause. However, the role of PLA2 activity and many of these downstream PLA2 products has received relatively little attention.
At the present time, there is no cure for MS. Current therapies are aimed at alleviating the symptoms of the disease and arresting its progress, as much as possible. Depending upon the type, drug treatment usually entails the use of disease-modifying agents such as the interferons (interferon beta 1-a, beta 1-b and alpha 2), glatiramer acetate or corticosteroids such as methylprednisolone and prednisone. Also, chemotherapeutic agents, such as methotrexate, azathioprine, cladribine, cyclophosphamide and cyclosporine, have been used. All of the above treatments have side-effect liabilities, little or no effect on fatigue and depression, as well as limited effects on relapse rates and on ability to prevent exacerbation of the disease. Treatment with interferons may also induce the production of neutralizing antibodies, which may ultimately decrease the efficacy of this therapy.
Current and planned disease modifying therapies for MS (in use or in trials) suppress aspects of the acquired immune response. The activities of the two front line treatments, Glatiramer acetate and Interferon beta, are not fully understood, but these operate at least in part by regulation of T cell proliferation and apoptosis. Natalizumab (TSAYBRI, Biogen), a humanized IgG4 antibody that binds to alpha-4 integrins, interferes with transvascular migration of immune reactive cells including T cells. Newer oral compounds, now in trials (e.g., FTY720, Novartis; BG-12, Biogen; Laquinimod, Teva, Mitoxantrone, Wyeth), are also designed to inhibit immune cell proliferation and/or trafficking. The drawbacks of this general approach are increasingly apparent. Either the drug has limited effectiveness or, with increasing efficacy, normal immune surveillance is compromised. For example, the cost effectiveness of Interferon beta is low when measured in terms of Quality Adjusted Life Years (QALY takes into account both EDSS score and longevity). On the other hand, Natalizumab appears to be very effective in limiting relapses, but was withdrawn during clinical trials because of cases of progressive multifocal leukoencephalopathy, a rare but often fatal disease resulting from opportunistic JC virus infections. CHEC-9 is an anti-inflammatory and neuron survival-promoting peptide. In the first instance, it inhibits enzymes that initiate a cascade of changes during the early stages of inflammation, so like other drugs that operate in this pathway (e.g. the COX inhibitors), it may have minimal effects on critical functions of the acquired immune response. On the other hand, it is possible that elimination of the early inflammatory component of MS will limit subsequent events in the cascade such as BBB breakdown, effusion of immune cells, myelin and axonal degeneration, and thereby inhibit active disease. Our data show that PLA2 inhibition limits these events after acute lesions of the nervous system. The same may be true in EAE, as suggested by our results and the results of others. Since CHEC-9 is an uncompetitive inhibitor, we propose it operates “as needed” when enzyme and substrate levels are high. In addition, the direct cell survival-promoting properties of CHEC-9 may further indicate its potential efficacy in MS, especially in light of new models of the disease that highlight the primary importance of cell degeneration (both neuronal and oligodendrocytic).
Recent studies of rodent experimental autoimmune encephalomyelitis (EAE) models of MS suggest PLA2 enzymes are involved in the genesis of both the behavioral deficits and the inflammation that characterize this disease. Pinto, et al. report that systemic infusion of substrate-like molecules, presumably targeting secreted (s)PLA2s, is effective in reducing inflammation and clinical EAE disease. However, the status of MS patients with regard to PLA2 activity is unknown, so it is not clear whether these enzymes are indeed a worthwhile target for MS treatment.
Despite the foregoing developments, there is a need for a method which provides a non-invasive method of discovering and monitoring inflammation and neuron degeneration. Moreover, there still exists a strong need for new treatments to combat the progression and symptoms of MS. The present invention meets these needs.